TWI421266B - Polymeric cell sheets for light guide plate materials, methods for their manufacture and use thereof - Google Patents

Description

Polyurethane sheet for light guide plate material, method for producing the same, and use thereof

The present invention relates to a polyurethane sheet for a light guide plate material and a method for producing the same, and a polyurethane for a light guide plate which is excellent in dimensional stability at a high temperature and excellent in flexibility while maintaining light transmittance in detail. Sheet and method of making the same.

Conventionally, as a film material of a light guide plate used for an LED backlight, a PMMA resin having excellent light transmittance is mainly used. However, since it is difficult to be thin, it has disadvantages such as poor flexibility and fragility, so polycarbonate, polyester, and poly are used. Aminoformate and the like.

However, since polycarbonate or polyester has high hardness, in applications requiring flexibility (flexibility), for example, a digital key backlight or the like, there is a disadvantage that the performance such as a click feeling is slightly inferior.

In addition, "digital key backlight" refers to a component that is placed under the numeric keys of a portable telephone or a numeric keypad of a notebook type personal computer to perform a task of causing the numeric keys to emit light. In addition, the "click feeling" refers to a concave touch of a button that is transmitted to a finger when an operation button such as a numeric key is pressed, and if a click feeling is obtained, the operator is likely to have a sense of realism at the time of operation. When the material of the digital key backlight is soft, the click feeling is obtained by following the recess of the button portion. However, if it is hard, the recess of the button portion is difficult to convey, and it is difficult to obtain a click feeling, so it is evaluated as "click feeling difference".

Although this shortcoming can be improved by thinning, if it is too thin, there is 1. Difficulty in processing, 2. Problems in reducing the amount of light entering the function, etc.

On the other hand, compared with polycarbonate or polyester, a polyurethane has a low hardness and can maintain flexibility even if it has a certain thickness. In this case, in order to obtain optical characteristics, an aliphatic or alicyclic diisocyanate is generally used as a raw material, which is not yellowish or hard to yellow, but shrinkage (collapse) due to heat generation, The dimensional stability at a high temperature of 80 ° C or higher is poor.

Patent Document 1 discloses that a reaction raw material composed of a polyol component containing a diol and a trifunctional or higher polyhydric alcohol and a polyisocyanate component containing a diisocyanate and a trifunctional or higher polyisocyanate is mixed and reacted in glass or plastic. When the protective layer of the polyurethane is formed on the surface, the protective film is excellent in abrasion resistance and excellent in stain resistance.

However, in this technique, there is a problem that a polyurethane sheet for a light guide plate which is excellent in dimensional stability at a high temperature and excellent in flexibility, which is excellent in flexibility, is not obtained.

The present inventors have examined the reason for this and found that the specific designation of the polyol component and the specific designation of the polyisocyanate component are important, and only the organometallic catalyst or the tertiary amine compound disclosed in Patent Document 1 is used. The catalyst system is incapable of solving the problem, and the selection of the crosslinking agent is extremely important, and the above-mentioned problems can be solved by organically combining these three, and it is possible to obtain a high-temperature dimensional stability and flexibility while maintaining light transmittance. The present invention is achieved by using a sheet of a polyurethane sheet which is excellent in a light guide plate.

Prior technical literature

Patent literature

Patent Document 1: Japanese Patent Publication No. 1-056717

An object of the present invention is to provide a polyurethane sheet for a light guide plate which is excellent in dimensional stability at a high temperature while maintaining light transmittance, and a method for producing the same, and a method for producing the same.

Further, other problems of the present invention will become apparent from the following description.

The above problems can be solved by the following inventions.

The invention described in claim 1 is a polyurethane sheet for a light guide plate material characterized by being composed of a polypropylene glycol ether (MW (average molecular weight): 500 to 1,500) and an alicyclic diisocyanate. In the prepolymer, polycaprolactone triol (MW: 350 to 800) as a crosslinking agent is blended to form a flake.

The invention described in claim 2 is a use of a polyurethane sheet for a light guide plate material, which is characterized in that the light guide plate material of claim 1 is treated with a polyurethane sheet as a number. Key backlighting is used.

The invention described in claim 3 is a method for producing a polyurethane sheet for a light guide plate material, characterized in that an alicyclic diisocyanate is added to a polypropylene glycol ether (MW: 500 to 1500) to produce an amine. The urethane prepolymer is blended with polycaprolactone triol (MW: 350 to 800) as a crosslinking agent in the urethane prepolymer to form a sheet.

The invention of claim 4 is the method for producing a polyurethane sheet for a light guide plate material according to claim 3, wherein the use of a light guide plate material for a polyurethane sheet is used for a digital key backlight .

According to the present invention, it is possible to provide a polyurethane sheet for a light guide plate which is excellent in dimensional stability while maintaining high light transmittance while maintaining high light transmittance, a method for producing the same, and a method for producing the same.

Form of implementing the invention

Hereinafter, embodiments of the present invention will be described.

The polyurethane sheet for a light guide plate material of the present invention is used in a prepolymer composed of a polypropylene glycol ether (MW (average molecular weight): 500 to 1500) and an alicyclic diisocyanate. The polycaprolactone triol (MW: 350 to 800) of the mixture is formed to form a sheet.

Here, the method of measuring the average molecular weight MW is calculated from the hydroxyl value.

In the present invention, a polycaprolactone triol or a urethane prepolymer is blended in such a manner that the NCO/OH molar ratio is from 0.95 to 1.20.

In the present invention, the component ratio of the prepolymer is preferably from 80 to 150 parts by weight, preferably from 100 to 140 parts by weight, per 100 parts by weight of the polypropylene glycol ether. .

As the polypropylene glycol ether used in the present invention, those having an average molecular weight of from 500 to 1,500 are preferably used, and those having an average molecular weight of from 800 to 1200 are preferably used.

When the molecular weight of the polypropylene glycol ether is too large as the above range, the transparency is poor, and if it is too small, the flexibility is poor.

The alicyclic diisocyanate used in the present invention may, for example, be an alicyclic diisocyanate such as hydrogenated diphenylmethane diisocyanate or isophorone diisocyanate, and preferably hydrogenated diphenylmethane diisocyanate.

In the present invention, the aromatic diisocyanate is not selected and the alicyclic diisocyanate is selected because the yellowing is maintained, and the transparency can be maintained for a longer period of time.

Further, in the present invention, the polycaprolactone triol used as the crosslinking agent is selected from those having an average molecular weight of from 350 to 800, preferably from 350 to 500, more preferably from 350 to 500. The range of 400.

When polycaprolactone triol having an average molecular weight of 350 to 800 is selected, dimensional stability (heat resistance) at a high temperature and excellent film forming property due to resin viscosity can be obtained.

If the average molecular weight is less than 350, the flexibility is poor, and it is not suitable for the light guide plate as required in the present invention.

Further, in the present invention, it is also preferred to previously add a catalyst to the polycaprolactone triol, and to use the mixed master batch as a crosslinking agent.

The urethane sheet for a light guide plate material of the present invention may have various thicknesses depending on the application. However, considering the use of a digital key backlight, a touch panel, etc., the preferred thickness is The range of 0.05 to 0.3 mm is more preferably in the range of 0.1 to 0.2 mm.

In the present invention, by selecting polycaprolactone triol having an average molecular weight of 350 to 800, since the wall thickness is thin as described above, heat resistance is obtained, and the amount of light incident is reduced, so that good function can be obtained. The thin walled light guide material is made of a polyurethane sheet.

In the present invention, if the ether triol is used without using the polycaprolactone triol having the specific molecular weight described above, the heat resistance of the present invention and the excellent film forming property due to the resin viscosity cannot be obtained.

In the present invention, the above-mentioned specific crosslinking agent is blended in the prepolymer formed from the specific polyol component and the specific polyisocyanate component, and the two are used (prepolymer and crosslinking agent). The polymerization is carried out by branching, and the polymerization by the ternary urethanation reaction is caused, and since it is organically bonded, the light guide plate having excellent dimensional stability at high temperature and excellent flexibility can be obtained. A urethane sheet.

In the present invention, a metal complex such as di-n-butyltin dilaurate or dioctyltin dilaurate may be blended as an antistatic agent in a range which does not impair the effects of the present invention. A metal salt compound such as a guanamine or a quinone group, or an additive such as a phenol-based or benzophenone-based UV absorber.

The polyurethane elastomer constituting the polyurethane sheet for a light guide plate of the present invention has a hardness (JIS-A; Duro A) in the range of 70 to 97, and is in a stress-elongation curve at 25 ° C. There is no relief point, and it has a transparent non-yellowing type thermosetting polyurethane elastomer having a light transmittance of 85% or more.

If the hardness is less than 70, it becomes too soft and the operation is difficult, and the heat resistance is also deteriorated. When the hardness is larger than 97, a drop point occurs in the stress-elongation curve at 25 ° C, and the flexibility is lacking.

In the present invention, the stress-elongation measurement was carried out by forming a sheet having a thickness of 2 mm by the blending of the present invention, and the dumbbell-shaped No. 5 shape of JIS K6251 was produced, and the sheet was stretched at a speed of 50 mm/min.

Further, since the polyurethane sheet for a light guide plate material of the present invention is excellent in flexibility, it can have optical characteristics in a portion where movement is required, and a good click feeling can be obtained in a numeric key or the like.

Further, it is relatively inexpensive compared to ruthenium or the like, and has a small dimensional change at a high temperature, and can be used up to 85 ° C, and has resistance to keying.

In addition, in the present invention, the button resistance test is carried out under the conditions of a probe RΦ of 2.0 mm (urethane) and 400 g of 2 million times, and the case where there is no damage even if there is unevenness is regarded as having Resistance to keying.

The urethane sheet of the light guide plate material of the present invention is particularly preferably used for a digital key backlight, and more preferably a digital key backlight for a portable telephone.

The method for forming the polyurethane sheet for a light guide plate material of the present invention is not particularly limited, and any of the sheets for forming a light guide plate, such as compression molding, injection molding, transfer molding, or extrusion molding, may be used. A method.

Example

The effects of the present invention are exemplified below by way of examples.

Example 1

<Preparation of polyurethane sheet>

100 parts by weight of polypropylene glycol ether (MW: average molecular weight 1000) was heated to 80 ° C, and then charged into a reactor preheated to 80 ° C, and 137 parts by weight of hydrogenated diphenylmethane diisocyanate was added while stirring. The reaction was allowed to proceed for 4 hours to give a urethane prepolymer. This urethane prepolymer was cooled once to return to 25 °C.

Further, 800 ppm of catalyst dilauric acid was added to polycaprolactone triol having an average molecular weight of 375, and mixed to form a crosslinking agent.

The urethane prepolymer and the crosslinking agent were mixed at room temperature for 1 minute at a temperature of NCO/OH=1.07, and after defoaming for 5 minutes, they were allowed to flow onto the polypropylene sheet by means of a doctor blade. To adjust to 0.2mm.

The sheet was heated at 90 ° C for 10 minutes to be semi-hardened, and then at 80 ° C for 6 hours to completely harden.

The polypropylene sheet was peeled off from the obtained formed sheet to serve as a sheet of a polyurethane sheet for a light guide plate of the present invention.

The physical properties of this polyurethane sheet were evaluated by the following evaluation methods.

<Evaluation method>

1. Spectral light transmittance (evaluation of light transmittance)

In the UV (ultraviolet)-VIS (visible light) spectrum, the transmittance at a wavelength of 400 nm, 500 nm, and 600 nm is 90% or more, and the evaluation is "○", and 85% or more and less than 90% is evaluated as "△". , 85% was evaluated as "X", and the results evaluated were shown in Table 1.

2. 85 ° C dimensional change (evaluation of dimensional stability of high temperature)

The prepared polyurethane sheet was a test piece of 0.2 mm thick and 50 mm × 50 mm, and when the change in size at 85 ° C was 50 mm ± 0.2 mm or less, it was evaluated as "○", and when it was 50 mm ± 0.2 mm or more , the evaluation is "x", and the results of the evaluation are shown in Table 1.

3. Flexibility

In the case of the JIS No. 5 dumbbell shape, whether there is a drop point in the stress-elongation curve (25° C., 50 mm/min), the case where none is evaluated as “○”, and the case where it is evaluated as “×”, which is shown in Table 1. The results of the evaluation.

4. Button properties

The button test was carried out under the conditions of a tentacity of RΦ2.0 mm (urethane) and 400 g of 2 million times. When the unevenness and the damage were evaluated, "○" was evaluated, and the unevenness was observed, but there was no damage, and there was no problem in practical use. In the case of "△", the damage was evaluated as "X", and the results of the evaluation are shown in Table 1.

Comparative example 1

The average molecular weight of the polycaprolactone triol of Example 1 was 300, and the same was used as a polyurethane sheet. Table 1 shows the results of evaluation in the same manner as in Example 1.

Comparative example 2

Using a mold, the thermoplastic non-yellowing yellow polyurethane pellets were hot pressed at 190 ° C and 20 MPa by a hot press for 5 minutes to form a 0.2 mm thick sheet, at 25 ° C × The 350 hrs annealer was evaluated in the same manner as in Example 1, and the results evaluated are shown in Table 1.

Comparative example 3

A sheet of 0.2 mm thick smooth polyethylene terephthalate was used as Comparative Example 3, and the results of evaluation in the same manner as in Example 1 are shown in Table 1.

As is apparent from Table 1, the polyurethane sheet for a light guide plate material of the present invention has a light transmittance of 85%, a dimensional change at 85 ° C (excellent heat resistance), and excellent flexibility. Further, it was found that in the button resistance test, since no breakage occurred, a sufficient function as a light guide plate for a digital key backlight was obtained.

In Comparative Example 1, the average molecular weight of the polycaprolactone triol was small, and the flexibility was poor, and the light guide plate material of the present invention could not be used.

It is understood that Comparative Example 2 is not a thermosetting property of the present invention, and since thermoplasticity-free yellowing-free polyurethane pellets are used, heat resistance is poor (dimensional change occurs at 85 ° C), and in the resistance test, The sheet is broken, and the strength of the light guide plate for the digital key backlight is not obtained.

In Comparative Example 3, since a sheet of smooth transparent polyethylene terephthalate was used, flexibility was poor.

Claims (4)

A polyurethane sheet for a light guide plate material, characterized in that it is used as a crosslinking agent in a prepolymer composed of a polypropylene glycol ether having a weight average molecular weight of MW of 500 to 1500 and an alicyclic diisocyanate. The polycaprolactone triol having a weight average molecular weight MW of 350 to 800 is formed into a flake shape. A use of a polyurethane sheet for a light guide plate material, characterized in that the light guide plate material of the first application of claim 1 is used as a ten key backlight with a polyurethane sheet. A method for producing a polyurethane sheet for a light guide plate material, characterized in that an alicyclic diisocyanate is added to a polypropylene glycol ether having a weight average molecular weight MW of 500 to 1,500 to produce a urethane prepolymer, Polycaprolactone triol having a weight average molecular weight MW of 350 to 800 as a crosslinking agent is blended in the urethane prepolymer, and is formed into a flake shape. A method for producing a polyurethane sheet for a light guide plate material according to claim 3, wherein a light guide plate material is used for the backlight of the digital key with a polyurethane sheet.